Cognitive Deficits Post-Traumatic Brain Injury and Their Association with Injury Severity and Gray Matter Volumes

Traumatic brain injury (TBI) is known to have a substantial though highly variable impact on cognitive abilities. Due to the wide range of cognitive abilities among healthy individuals, an objective assessment of TBI-related cognitive loss requires an accurate measurement of pre-morbid cognitive performance. To address this problem, we recruited 50 adults who sustained a TBI and had performed a cognitive baseline assessment in adolescence as part of the aptitude tests mandated by the Israeli Defense Forces. This group was matched with non-injured controls (n = 35). Pre- and post-injury cognitive assessments consisted of three domains-namely, verbal abstraction, mathematical reasoning, and non-verbal abstract reasoning (from the Wechsler Adult Intelligence Scale-Third Edition). The difference between post- and pre-injury scores was calculated as a measure of domain-specific cognitive decline. Voxel-based regression was used to correlate cognitive decline with modulated gray matter probability maps controlling for age, Glasgow Coma Scale, and total intracranial volume. Using objectively assessed cognitive scores, we found that abstract reasoning declined in both moderate-severe and mild TBI patients, whereas verbal abstraction declined only in the moderate-severe group. Mathematical reasoning was not affected by TBI. In the TBI patients, non-verbal abstract reasoning post-pre-injury change scores were negatively correlated with the volume of the insula. We conclude that access to pre-morbid neuropsychological data may have facilitated the discovery of the effects of mild TBI on abstract reasoning, as well as a significant correlation between TBI-related decline in this cognitive domain and the volume of the bilateral insula, both of which had not been appreciated in the past.